This invention relates to an internal combustion engine and more particularly to an improved ignition control for an internal combustion engine and particularly one embodying direct cylinder injection.
In the interest of improving the performance of an internal combustion engine, direct cylinder injection has been resorted to. By injecting fuel directly into the combustion chamber of the engine, a number of advantages can be accomplished. One of these advantages it the ability to run the engine on less than stoichiometric mixture. This generally is referred to as "lean burn".
This is done primarily by stratifying the fuel air mixture in the combustion chamber. When stratification is employed, the goal is to have a stoichiometric mixture present at the gap of the spark plug at the time of firing. This will ensure the initiation of combustion. The remainder of the charge in the combustion chamber need not be stoichiometric and hence, it is possible to obtain improved fuel economy and exhaust emission control if stratification can be successfully accomplished.
A problem in connection with achieving stratification, however, is that the stoichiometric patch of fuel must be at the spark gap at the time of firing and must be capable of being burned. This frequently gives a problem, particularly under a number of running conditions where the total charge in the combustion chamber is much less than stoichiometric.
Various arrangements have been proposed in order to ensure that the stoichiometric mixture is present at the spark gap at the time of firing. Even these, however, do present some difficulties.
It is, therefore, a principal object of this invention to provide an improved engine control system that permits operation on a lean fuel air charge.
It is a further object of this invention to provide an improved method of operating a direct injected internal combustion engine.
In addition to the ability to obtain better stratification, direct cylinder injection also has other advantages. However, like most features in engine design, there are trade-offs that result. That is, there are some areas where direct cylinder injection may have problems regardless of whether stratification is accomplished or even desired.
One of the problems with direct cylinder injection is to control the pressure of the fuel that is injected and to avoid impingement of the fuel on surfaces in the combustion chamber which may be at either too high or too low a temperature. If the temperature is too high where the fuel is injected, combustion may occur before the desired time. If the temperature is too low, the mixture may not ignite even though it is rich enough to ignite under normal conditions.
It is, therefore, a still further object of this invention to provide an improved engine control for an engine having direct injection wherein it will be ensured that the mixture is ignited and completely burned.
It is a further object of this invention to provide an improved ignition system, an ignition control system for a direct injected engine.
One type of engine that can benefit significantly from direct injection is a two-cycle engine. Two-cycle engines because of their porting overlap do present significant problems in exhaust emission control. Direct cylinder injection can be utilized to more closely control the amount of fuel and the emission control.
One problem with direct injection, however, is that at times the fuel may be injected when the exhaust port is open. If this is done, there is a risk that fuel can escape out of the exhaust port before it has been burned.
It is, therefore, a still further object of this invention to provide an improved direct injection system for a two-cycle engine and associated engine control that will ensure that fuel cannot escape from the combustion chamber before it has had an opportunity to burn.
One of the disadvantages of direct cylinder injection with both two and four cycle engines is that the fuel injectors are generally more expensive and more prone to developing problems than with manifold injection. This is because the injector is normally exposed directly to the combustion in the combustion chamber. This requires higher cost injectors and also raises the problem of contamination or damage to the injector.
It has been proposed, therefore, to position the fuel injector in an area where it will be shielded by the piston during at least the initial combustion phase. In this way, the lower cost injectors can be employed and the injector is less likely to become contaminated. However, this then raises the additional problem that the time for fuel injection is shortened. Thus, it may be difficult to provide adequate fuel for complete combustion, particularly when operating on a two-stroke cycle.
It is, therefore, a still further object of this invention to provide an improved injection and engine control system for a direct injected engine wherein the injector is shielded during at least a portion of the combustion cycle.
One way of ensuring good and/or complete combustion, particularly when operating in a stratified charge mode has been to extend the duration of spark firing and/or changing the energy level during firing. The spark duration can be extended by various methods one of which includes multiple firing of the spark plug. Such an arrangement is disclosed in the U.S. Pat. No. 5,170,760 issued Dec. 15, 1992 and entitled "Ignition System For Two-Cycle Engine." Basically, that control determines whether the engine is operating on either a homogeneous mixture or a stratified mixture. The spark control is based primarily on this determination.
It has been found, however, that although that system is effective, the switching between multiple firing and single firing need not depend solely or even primarily on whether the mixture is stratified or homogeneous. In fact, it has been found that other running conditions may dictate multiple firings and the optimum number of firings may vary depending upon a wide variety of running conditions.
It is, therefore, a further principal object of this invention to provide an improved ignition control for an engine having direct cylinder injection wherein the spark control varies between single and multiple ignitions and the number of multiple ignitions is varied depending upon a wide variety of engine running conditions.